Polyamide has been utilized extensively as a synthetic fiber. While its structural and mechanical properties make it attractive for use in such capacities as carpeting, it is nonetheless relatively expensive. It would therefore be desirable to replace a portion of polyamide fibers with a core formed from a relatively lower cost material.
In this regard, some polymeric materials that are attractive candidates as a partial replacement of the polyamide are "off-specification"--that is, contain a contaminant. For example, "off-specification" nylon-6 having relatively high levels of the cyclic dimer of caprolactam is particularly troublesome when attempted to be melt-spun. Such "off-specification" nylon 6 can be obtained from a number of sources due, for example, to its being manufactured with methods that produce high levels of the cyclic dimer contaminant, or have avoided (or minimally exposed) to a dimer extraction step. However, replacing a portion of a 100% polyamide fiber with a core portion of a contaminant material may affect the mechanical properties of the fiber to an extent that it would no longer be useful in its intended end-use application (e.g., as a carpet fiber).
Furthermore, many regenerated polymeric materials are already colored (e.g., by use of a colorant or dye). Therefore, their use as a material to make useful products (e.g., carpet fibers) is usually limited by the color of the regenerated polymeric materials that may be obtained. Typically, only clear regenerated polymeric materials are employed for such purposes since the manufacturer can then add pigments or dyes to provide products of desired color.
Recently, U.S. Pat. No. 5,549,957 has proposed multi-lobal composite fibers having a nylon sheath and a core of a fiber-forming polymer which can be, for example, "off spec" or reclaimed polymers. (Column 4, lines 6-8.) The core can be polypropylene, polyethylene terephthalate, high density polyethylene, polyester or polyvinyl chloride. (Column 4, lines 17-20.) The core is covered with a sheath of virgin nylon which constitutes between 30% to 50% by weight of the core/sheath fiber. (Column 3, lines 65-67.)
The presently known prior art therefore evidences the fact that contaminant-containing polymeric materials--particularly, nylon-6 having a relatively high level of the cyclic dimer of caprolactam--have not been employed as a structural component of finished bicomponent synthetic fiber structures.
Broadly, the present invention relates to a bicomponent fiber structure having a polyamide domain and another distinct cross-sectional domain formed of polymeric material having a relatively high level of contaminant. The contaminant-containing polymeric domain is embedded entirely within, and thus completely surrounded by, the polyamide domain. Preferably, the fibers of this invention have a concentric sheath-core structure whereby the polyamide domain forms the sheath and the contaminant polymer forms the core. Surprisingly, even though the core is formed of a polymer having relatively high levels of contaminant, the bicomponent sheath-core fibers of this invention exhibit properties which are comparable in many respects to fibers formed from 100% (virgin) polyamide.
In another aspect, the present invention relates to a bicomponent fiber structure having a polyamide domain and another distinct cross-sectional domain formed of a regenerated colored polymeric material. The regenerated polymeric domain is embedded entirely within, and thus completely surrounded by, the polyamide domain. Preferably, the fibers of this invention have a concentric sheath-core structure whereby the polyamide domain forms the sheath and the regenerated polymer forms the core. Surprisingly, even though the core is formed of a regenerated colored polymeric material, the bicomponent sheath-core fibers of this invention exhibit properties which are comparable in many respects to fibers formed from 100% (virgin) polyamide. For example, the virgin polymer sheath component of the bicomponent fibers of this invention can be colored to an extent that the colored regenerated polymeric core material in the core is "hidden".
A further aspect of this invention is that the colored regenerated polymeric material be blended with a color-leveler--for example, a black pigment, such a carbon black. In this regard, it is known that most regenerated (recycled) polymeric materials will have some color variation, typically a shade of gray-green. According to the present invention, therefore, the regenerated colored polymeric material would first be measured against a known color standard. A specified amount of a color leveler (e.g., carbon black) would then be added to the regenerated colored polymeric material to correct its color to the known standard. Thereafter, the color-corrected regenerated polymeric material may be incorporated into the core of a sheath-core fiber according to this invention.
These, as well as other aspects and advantages of this invention, will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.